1. Field of the Invention
This invention relates to an apparatus for needling a nonwoven web comprising at least one needle board provided with a multiplicity of needles, a backing member facing the needle board and spaced therefrom, and a stripper, which is disposed between the backing member and the needle board, wherein said stripper and optionally also the backing member comprises a perforated plate that is formed with holes, the needles are movable through said holes and are arranged in groups, and a hole in the perforated plate of the stripper and a hole in the optional perforated plate of the backing member is commonly associated with the needles of each of said groups.
2. Description of the Prior Art
To ensure that a nonwoven web will be uniformly needled, a uniform distribution of the needle penetrations over the width of the nonwoven web is desired. For this reason the pitch of the needles in the direction of the working width of the needling apparatus is uniform and the pitch of the holes in the perforated plate of the stripper and the pitch of the holes of any perforated plate of the backing member in said direction is uniform too and is equal to said needle pitch. For that purpose the needles and the holes associated with respective needles formed in the perforated plate and associated with respective needles are arranged in uniformly spaced apart transverse rows and have a uniform pitch in each of said rows. The spacing of said transverse rows and the hole pitch in each of said transverse rows are selected to provide for a hole spacing in excess of a minimum hole spacing required for structural reasons. The rows of holes are staggered relative to each other. Whereas such an arrangement will provide a uniform pitch of the needles in the direction of the working width, the occurrence of surface textures which visibly disturb the appearance of the surface of the needled webs, particularly in larger areas, cannot be precluded thereby.
If the individual needles are not mounted in the needle board in respective bores in the needle board but groups of needles are mounted either in a common bore in the needle board or in a common shank holder, which is mounted like a single needle in a bore in the needle board (British Patent Specification 1,327,993; French Patent Specification 2,138,069), and if the perforated plate of the stripper and any perforated plate of the backing member is formed with holes associated each with the commonly held needles, it will be possible to achieve a locally increased needle density. But the problem to avoid a surface structure in the nonwoven web will not be solved thereby because the bores provided in the needle board for receiving the shanks of respective groups of needles are again uniformly distributed. Besides, the needles contact each other in part so that the needle pitch in each group of needles is very small and the gaps between the needles may become clogged with fibers.